Printhead high side switch controls

ABSTRACT

In example implementations, an apparatus is provided. The apparatus includes a power supply, a first switch coupled to the power supply, a second switch coupled to the first switch, a third switch coupled to the power supply, the first switch, and the second switch, and a resistor coupled to the third switch. The first switch is to be controlled via a high voltage logic. The second switch is to be controlled via a low voltage logic. The resistor is to generate heat when energized. The first switch and the second switch are to control activation of the third switch to energize the resistor and cause a nozzle chamber to dispense a printing fluid.

BACKGROUND

Printers are used to print images onto a print medium. Printers mayprint images using different types of printing fluids and/or materials.For example, some printers may use ink, toner, and the like. A print jobmay be transmitted to the printer and the printer may dispense theprinting fluids and/or materials on the print medium in accordance withthe print job.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a printer that is deployed with an exampleof the high side switch (HSS) control or circuit block of the presentdisclosure;

FIG. 2 is a block diagram of an example nozzle chamber that iscontrolled by the HSS control of the present disclosure;

FIG. 3 is a block diagram of an example HSS control of the presentdisclosure;

FIG. 4 is a circuit diagram of an example HSS control of the presentdisclosure;

FIG. 5 is an example of a plurality of primitives with a plurality ofHSS controls of the present disclosure; and

FIG. 6 illustrates a flow chart of an example method to activate athermal ink jet resistor using an HSS control of the present disclosure.

DETAILED DESCRIPTION

Examples described herein provide a high side switch (HSS) control for aprinthead. As discussed above, printers can use various types of systemsand printing fluids to print images onto a print medium. One example canbe a thermal ink jet (TIJ) printer that uses TIJ printheads. However,the present disclosure may apply to two-dimensional printers as well asthree dimensional printers.

A TIJ printhead may include a nozzle chamber that includes a TIJresistor that can generate heat when energized. The heat generated fromthe TIJ resistor may heat the printing fluid to create a steam bubbleinside of the nozzle chamber that pushes the drop of printing fluid outof the nozzle chamber.

Different types of controls can be used to control activation of the TIJresistor. Examples of the controls may include a low side switch (LSS)control and a high side switch (HSS) control. The LSS may provide alower relative cost in terms of an amount of silicon area allocated tothe circuits for controlling the LSS and the LSS itself. However, insome cases the LSS may provide no energy regulation against variation inpower supply voltage, can have a reduced resistor life due to constantbias between the ink at ground and resistor at a voltage input, and thefunctionality of an entire group of resistors can be compromised if asingle resistor shorts out.

In contrast, the HSS may provide solutions to the above issues with theLSS control. Namely, the HSS may provide energy regulation, someisolation to reduce the bias, and isolate damage to a single resistor ifthe resistor shorts out. However, the HSS uses a field effect transistor(FET) level shifter that may consume more silicon space, and it maytherefore cost more to produce than the LSS. For example, the levelshifter can consume as much as thousands of square microns of siliconarea per nozzle.

In addition, some HSS control designs can use custom fabricatedtransistors or devices (e.g., non-industry standard devices). Thesecustom devices can make it difficult to efficiently fabricate the HSScontrols using standard circuit manufacturing processes in theintegrated circuit industry.

Some HSS control designs may also use level shifters, which can drawhundreds of micro amps of current even when the nozzles are not firing.Multiplied by thousands of nozzles, the total amount of current that canbe drawn in an idle state can be prohibitive.

The present disclosure provides a circuit design for the HSS controlthat reduces the amount of silicon that is used by simplifying thedesign of the HSS control. The simplified design reduces the number ofhigh voltage p-type metal oxide semiconductor (HVPMOS) elements andchanges the level shifter design to eliminate current that can be drawnwhen the nozzles are idle. In addition, the HSS control of the presentdisclosure eliminates the components associated with a clamp circuit.The clamp circuit can be included to protect susceptible devices fromover-voltage events in the case of a fault or defect.

In addition, the HSS control of the present disclosure uses standarddevices rather than custom devices. As a result, the circuitmanufacturing processes to build the HSS control may be more availableand cheaper to build. The overall amount of silicon that is used isreduced, thereby reducing the overall cost of producing the HSS controlof the present disclosure.

FIG. 1 illustrates an example printer 100 of the present disclosure. Inone example, the printer 100 may be a thermal ink jet printer. Theprinter 100 has been simplified to show a cross-section of a fluidic die102 used to eject printing fluid onto a print medium. The printer 100may include additional components that are not shown, such as mechanicalcomponents associated with a print path, a feed module, a finishingmodule, a digital front end, a paper tray, reservoirs for the printingfluid, and the like.

In one example, the fluidic die 102 includes a bulk silicon substrate104. A layer of circuits 106 may be formed in and/or on the bulk siliconsubstrate 104. In one example, a high side switch (HSS) circuit block114 of the present disclosure may be formed on the layer of circuits106. The HSS circuit block 114 may be used to control the ejection ofprinting fluid from a nozzle 112 of the fluidic die 102. Each nozzle 112may be associated with a respective HSS circuit block 114. In otherwords, the fluidic die 102 may include a plurality of HSS circuit blocks114. The HSS 114 of the present disclosure is illustrated in FIGS. 3 and4 and discussed in further details below.

In one example, the fluidic die 102 may include an ink slot 108 and alayer of fluidics 110. Printing fluid may move through the ink slot 108to the desired nozzles 112 to be ejected onto a print medium.

FIG. 2 illustrates a cross sectional view of an example nozzle chamber200. Each nozzle 112 of the fluidic die 102 may be in fluidcommunication with a nozzle chamber 200. In one example, the nozzlechamber 200 may be coupled to the HSS 114. A portion of the nozzlechamber 200 may include a conductive plate 206. The conductive plate 206may be made of a conductive metal (e.g., tantalum). The conductive plate206 may be electrically isolated from other components in the nozzlechamber 200.

In one example, a resistor 204 may be positioned adjacent to theconductive plate 206 (also known as a cavitation plate). In one example,an oxide layer may be grown between the resistor 204 and the conductiveplate 206. When a printing fluid 202 is provided into the nozzle chamber200, the resistor 204 may generate heat when activated to form a steambubble 208. The steam bubble 208 may force the printing fluid 202 out ofthe nozzle 112.

The conductive plate 206 may protect the underlying structures from theforces associated with the steam bubble 208 forming and collapsing inthe nozzle chamber 200. The conductive plate 206 may also prevent theprinting fluid 202 from contacting the resistor 204 and otherelectrically insulating layers. If the printing fluid 202 were tocontact the resistor 204, a short would be formed, which may cause thenozzle chamber 200 to malfunction.

In one example, the HSS circuit block 114 of the present disclosure maybe used to control activation of the resistor 204. As noted above, theHSS circuit block 114 of the present disclosure provides a circuitdesign that is smaller and consumes less silicon in the bulk siliconsubstrate 104. The design of the HSS circuit block 114 of the presentdisclosure does not include a circuit clamp and a test circuit, whichcan consume large amounts of the silicon in the bulk silicon substrate104. The circuit clamp may be implemented in previous HSS controls toprotect susceptible devices from over-voltage events in the case of afault or defect.

Lastly, the design of the HSS circuit block 114 may use standardcomponents that are not custom built, and therefore, more compatiblewith available manufacturing processes. As a result, the cost to buildthe HSS circuit block 114, and the overall fluidic die 102 may besignificantly reduced.

Although an example of an ejecting actuator is illustrated in FIG. 2, itshould be noted that the HSS circuit block 114 can also be used tocontrol non-ejecting actuators (e.g., actuators that use micro-fluidicpumps). For example, the HSS 114 may be used to generate the steambubble 208 that can be used to move fluid through a channel.

FIG. 3 illustrates a block diagram of an example of the HSS circuitblock 114 of the present disclosure. In one example, the HSS circuitblock 114 includes a power supply 302. The power supply 302 may providehigh voltage. For example, the high voltage may be approximately greaterthan 10 volts. In one example, the high voltage may be approximately 30volts.

A first switch 304 may be coupled to the power supply 302. The firstswitch 304 may be a high voltage switch and may operate via a highvoltage signal. In one example, a high voltage switch may be a switchthat can switch high voltage (e.g., 30 volts), but is controlled by acontrol signal that varies between a high voltage and a voltagethreshold set by the low voltage signal. For example, if the highvoltage is 30 volts and the low voltage signal is approximately 3.3volts, then the high voltage switch may be controlled by a controlsignal that varies between 30 volts and approximately 27 volts.

The high voltage signal may be a digital logic signal generated by ahigh-voltage control block, which is powered by a high-voltage powersource, as illustrated in FIG. 5 and discussed in further details below.The gate of the first switch 304 may be controlled via a high voltagesignal that varies between a high voltage and the high voltage less thelow voltage signal. For example, if the low voltage signal isapproximately 3.3 volts, the gate of the first switch 304 may beactivated with a 27 volt signal or deactivated with a 30 volt signal.

In one example, a second switch 306 may be coupled downstream from thefirst switch 304. The second switch 306 may be a low voltage switch andmay operate via a low voltage signal. In one example, a low voltageswitch may be a switch that can switch high voltage (e.g., 30 volts),but is controlled with a low voltage signal. A low voltage signal may bea signal that switches between 0 and 5 volts or 0 and 3.3 volts.

The low voltage signal may be a digital logic signal generated by a lowvoltage control block, which is powered by a low voltage power source,as illustrated in FIG. 5 and discussed in further details below. Thesecond switch 306 may be activated with a 3.3 volt signal anddeactivated with a 0 volt signal.

In one example, a third switch 308 may be coupled to the power supply302. The third switch 308 may be a low voltage switch that is tolerantof high voltage differentials. The third switch 308 may be coupled tothe resistor 204. The resistor 204 may be the same resistor 204illustrated in FIG. 2 to generate heat and create the steam bubble 208to eject the printing fluid 202 out of the nozzle 112.

Although a single power supply 302 is illustrated in FIG. 3, it shouldbe noted that multiple power supplies 302 may be deployed to trade offdifferent levels of voltage regulation for power and thermal efficiency.For example, the first switch 304 and the third switch 308 may becoupled to separate power supplies 302.

In one example, the first switch 304 and the second switch 306 mayoperate in an inverse relationship to control activation of the thirdswitch 308. For example, when the first switch 304 is activated, and thesecond switch 306 is deactivated, the third switch 308 may be activatedto couple the output of the power supply 302 to the resistor 204. Whenthe third switch 308 is activated, the current may flow through thethird switch 308 and to the resistor 204. The current flowing throughthe resistor 204 may cause the resistor 204 to generate heat, form thesteam bubble 208, and eject the printing fluid 202, as described above.

In one example, when the first switch 304 is deactivated and the secondswitch 306 is activated, the third switch 308 may be deactivated. Inother words, the third switch 308 may decouple the power supply 302 fromthe resistor 204. As a result, no current flows through the third switch308 to the resistor 204, which turns off the resistor 204.

Notably, the HSS circuit block 114 of the present disclosure uses fewerhigh voltage switches of either NMOS or PMOS type compared to previousHSS designs. The high voltage switches may be larger and may consumemore of the silicon die. Thus, by reducing the number of high voltageswitches, the overall size of the HSS circuit block 114 may be smaller,may consume less silicon die, and may be cheaper to manufacture.

FIG. 4 illustrates a circuit diagram of an example of the HSS circuitblock 114 of the present disclosure. In one example, the HSS circuitblock 114 includes a power supply 402. The power supply 402 may providehigh voltage. For example, the high voltage may be approximately greaterthan 10 volts. In one example, the high voltage may be approximately 30volts. As noted above, although a single power supply 402 is illustratedin FIG. 4, two separate power supplies 402 may be implemented to providepower to the connected switches.

A high voltage p-type metal oxide semiconductor (HVPMOS) switch 404 maybe coupled to the power supply 402. The HVPMOS switch 404 may be a highvoltage switch that may be controlled via a high voltage signal. Thehigh voltage signal may be a digital logic signal generated by a highvoltage control block, which is powered by a high voltage power source,as illustrated in FIG. 5 and discussed in further details below. Thegate of the HVPMOS switch 404 may operate between a high voltage and thehigh voltage less a low voltage signal. For example, if the low voltagesignal is approximately 3.3 volts, the gate of the HVPMOS switch 404 maybe activated with 27 volt signal or deactivated with a 30 volt signal.

In one example, a single gate laterally diffused metal oxidesemiconductor (SGLDMOS) switch 406 may be coupled downstream from theHVPMOS switch 404. The SGLDMOS switch 406 may be a high voltage switchthat is controlled via a low voltage signal. The low voltage signal maybe a digital logic signal generated by a low-voltage control block,which is powered by a low voltage power source, as illustrated in FIG. 5and discussed in further details below. The SGLDMOS switch 406 may beactivated with a digital signal generated in response to a 3.3 voltsignal and deactivated with a digital signal generated in response to a0 volt signal.

In one example, a laterally diffused metal oxide semiconductor (LDMOS)switch 408 may be coupled to the power supply 402. The LDMOS switch 408may be an n-type switch that is controlled via a high voltage signal(e.g., the gate of the switch 408 may transition between 0-30 V). TheLDMOS switch 408 may be an efficient switch for controlling the heaterresistor 204.

The heater resistor 204 may be coupled to the LDMOS switch 408. When theLDMOS switch 408 is activated, current may flow across the LDMOS switch408 to the heater resistor 204. The heater resistor 204 may generateheat as current flows through the heater resistor 204 to create thesteam bubble 208, which causes the printing fluid 202 to be ejected fromthe nozzle chamber 200.

In one example, the HVPMOS switch 404 and the SGLDMOS switch 406 mayoperate in an inverse relationship to control activation of the LDMOSswitch 408. For example, when the HVPMOS switch 404 is activated, andthe SGLDMOS switch 406 is deactivated, the LDMOS switch 408 may beactivated to couple the output of the power supply 402 to the resistor204. When the LDMOS switch 408 is activated, the current may flowthrough the LDMOS switch 408 and to the heater resistor 204. The currentflowing through the heater resistor 204 may cause the heater resistor204 to generate heat, form the steam bubble 208, and eject the printingfluid 202, as described above.

In one example, when the HVPMOS switch 404 is deactivated and theSGLDMOS switch 406 is activated, the LDMOS switch 408 may bedeactivated. In other words, the LDMOS switch 408 may decouple the powersupply 402 from the resistor 204. As a result, no current flows throughthe LDMOS switch 408 to the heater resistor 204, which turns off theheater resistor 204.

Notably, the HSS circuit block 114 of the present disclosure uses asingle HVPMOS switch compared to previous HSS designs that use multipleHVPMOS switches. In addition, the HSS circuit block 114 of the presentdisclosure uses fewer high voltage switches of either NMOS or PMOS typecompared to previous HSS designs. The HVPMOS switches may be larger andconsume more of the silicon die. Thus, by reducing the number of HVPMOSswitches, the overall size of the HSS circuit block 114 may be smaller,may consume less silicon die, and may be cheaper to manufacture.

FIG. 5 illustrates an example of a plurality of primitives 522 with aplurality of HSS circuit blocks (e.g., HSS circuit blocks 114 _(1-n)) ofthe present disclosure. In one example, the fluidic die 102 may beorganized into a plurality of primitives 522 ₁ to 522 _(m) (hereinafteralso referred to individually as a primitive 522 or collectively asprimitives 522). Each primitive 522 may include a plurality of nozzlechambers 200 that are controlled by a respective HSS circuit block 114 ₁to 114 _(n). HSS circuit blocks 114 ₁-114 _(n) may each be implementedas illustrated in FIG. 3 or 4.

In one example, each primitive 522 may include a high voltage (HV) logic506 and a low voltage (LV) logic 508. The HV logic 506 may be coupled toa high voltage power supply 510 and a high voltage ground (HV GND). Thehigh voltage power supply 510 may provide 30 volts of power. The HVlogic 506 may be a high voltage device that operates with high voltageprovided by a high voltage power supply 510 and high voltage ground (HVGND). The HV logic 506 may generate a high voltage logic signal based ona high voltage signal received from a column level shifter 504. The highvoltage signal generated by the HV logic 506 may be used to control theHSS control circuit 114. For example, the high voltage logic signalgenerated by the HV logic 506 may be sent to the gate of the firstswitch 304 or the HVPMOS switch 404 to toggle the gate.

The LV logic 508 may be a low voltage device that operates with lowvoltage provided by a low voltage power supply 512 and a low voltageground (LV GND). The low voltage power supply 512 may provide 5 volts ofpower. The LV logic 508 may generate a low voltage logic signal based ona low voltage signal received from the column level shifter 504. The lowvoltage signal generated by the LV logic 508 may be used to control theHSS control circuit 114. For example, the low voltage logic signalgenerated by the LV logic 508 may be sent to the gate of the secondswitch 306 or the SGLDMOS switch 406 to toggle the gate.

In one example, the HV logic 506 may be communicatively coupled to HVlogic 506 of other primitives 522. For example, the HV logic 506 mayinclude a communication path 514 to the next primitive (e.g., primitivem+1) and a communication path 516 from the previous primitive (e.g.,primitive m−1). Notably, the HV logic 508 in the first primitive 522 ₁may not have the communication path 516 and the HV logic 506 in the lastprimitive 522 _(m) may not have the communication path 514.

In one example, the LV logic 508 may be communicatively coupled to theLV logic 508 of the other primitives 522. For example, the LV logic 508may include a communication path 518 to the next primitive (e.g.,primitive m+1) and a communication path 520 from the previous primitive(e.g., primitive m−1). Notably, the LV logic 508 in the first primitive522 ₁ may not have the communication path 518 and the LV logic 508 inthe last primitive 522 _(m) may not have the communication path 520.

In one example, the primitives 522 may each be coupled to the columnlevel shifter 504 that is controlled by a controller 502. The controller502 may be a processor or an application specific integrated controller(ASIC) chip that operates with low voltage. The controller 502 mayprovide a low voltage signal to the column level shifter 504. The columnlevel shifter 504 may take the low voltage signals and generate a highvoltage version of the low voltage signals. For example, if there was alow voltage enable signal, the column level shifter 504 may generate ahigh voltage “copy” of the same low voltage enable signal. The lowvoltage signal from the controller 502 may be sent to the LV logic 508.The high voltage signal that is a copy of the low voltage signal fromthe column level shifter 504 may be sent to the HV logic 506.

FIG. 6 illustrates a flow chart of an example method to activate athermal ink jet resistor using an HSS control of the present disclosure.In an example, the method 600 may be performed by a controller orprocessor of the printer 100 illustrated in FIG. 1.

At block 602, the method 600 begins. At block 604, the method 600receives a signal to dispense a printing fluid from a nozzle chamber.For example, a printer may be activated to print a desired image onto aprint medium. A printer may determine locations on the print medium todispense a printing fluid. The printing fluid may be dispensed vianozzle chambers in a fluidic die.

At block 606, the method 600 transmits an enable signal to a firstswitch and a disable signal to a second switch coupled to the firstswitch in a high side switch control associated with the nozzle chamber,wherein the enable signal activates the first switch and the disablesignal deactivates the second switch to allow a voltage to flow throughfirst switch to activate a third switch, wherein the third switch allowsa current to flow through to a resistor when the third switch isactivated, wherein the resistor is to generate heat to dispense theprinting fluid from the nozzle chamber. For example, the printer maycause a high voltage logic to generate an enable signal to a control pinof the first switch to activate the gate of the first switch. Theprinter may also cause a low voltage logic to generate a disable signalto a control pin of the second switch to deactivate the gate of thesecond switch. When the first switch is activated, and the second switchis deactivated, the third switch may receive a high voltage (e.g., 30volts) to the control pin of the third switch to activate the gate ofthe third switch.

When the third switch is activated, the current from the power supplymay be allowed to flow through the resistor or the TIJ resistor. Thecurrent flowing through the resistor may cause the resistor to generateheat. The heat may cause a steam bubble to be formed inside of thenozzle chamber. The steam bubble may force the printing fluid throughthe nozzle and out of the nozzle chamber onto the print media.

In one example, a signal to stop the printing fluid from dispensing fromthe nozzle chamber may be received. For example, printing may becompleted at a particular location of the print media for the print job.

In response to the signal to stop the printing fluid from dispensing,the printer may cause a disable signal to be transmitted to the firstswitch and an enable signal to be transmitted to the second switch. Thedisable signal may be sent to the control pin of the first switch todeactivate the gate of the first switch. The enable signal may be sentto the control pin of the second switch to activate the gate of thesecond switch. When the first switch is deactivated and the secondswitch is activated, the third switch may receive a low voltage (e.g., 0volts) to the control pin of the third switch and deactivate the gate ofthe third switch. As a result, no current may flow through the thirdswitch or the resistor. When no current flows through the resistor, theresistor may stop generating heat, which may eliminate the formation ofthe steam bubble, and prevent the printing fluid from being ejected outof the nozzle chamber. At block 608, the method 600 ends.

It will be appreciated that variants of the above-disclosed and otherfeatures and functions, or alternatives thereof, may be combined intomany other different systems or applications. Various presentlyunforeseen or unanticipated alternatives, modifications, variations, orimprovements therein may be subsequently made by those skilled in theart which are also intended to be encompassed by the following claims.

1. An apparatus, comprising: a power supply; a first switch coupled tothe power supply, wherein the first switch is to be controlled via ahigh voltage logic signal; a second switch coupled to the first switch,wherein the second switch is to be controlled via a low voltage logicsignal; a third switch coupled to the power supply, the first switch,and the second switch; and a resistor coupled to the third switch togenerate heat when energized, wherein the first switch and the secondswitch are to control activation of the third switch to energize theresistor and cause a nozzle chamber to dispense a printing fluid.
 2. Theapparatus of claim 1, further comprising: a controller; and a columnlevel shifter coupled to the controller to generate a high voltagesignal copy of a low voltage signal to be provided by the controller. 3.The apparatus of claim 2, further comprising: a high voltage logiccoupled to the column level shifter; and a low voltage logic coupled tothe controller.
 4. The apparatus of claim 3, wherein the high voltagelogic is to provide the high voltage logic signal to the first switch.5. The apparatus of claim 3, wherein the low voltage logic to providethe low voltage logic signal to the second switch.
 6. The apparatus ofclaim 3, wherein the first switch, the second switch, the third switch,and the resistor are associated with a nozzle, wherein the high voltagelogic, the low voltage logic and a plurality of nozzles are associatedwith a primitive.
 7. The apparatus of claim 6, further comprising: aplurality of primitives coupled to the column level shifter, wherein arespective high voltage logic and a respective low voltage logic of eachone of the plurality of primitives are communicatively coupled.
 8. Theapparatus of claim 1, wherein the first switch and the second switchoperate in an inverse relationship to control the activation of thethird switch.
 9. An apparatus, comprising: a power supply; a highvoltage p-type metal oxide semiconductor (HVPMOS) switch coupled to thepower supply, wherein the HVPMOS is to be controlled via a high voltagelogic; a first laterally diffused metal oxide semiconductor (LDMOS)switch coupled to the HVPMOS switch, wherein the LDMOS switch is to becontrolled via a low voltage logic; a second LDMOS switch coupled to thepower supply, the HVPMOS switch and the first LDMOS switch; and aresistor coupled to the second LDMOS switch to generate heat whenenergized, wherein the HVPMOS switch and the LDMOS switch are to controlactivation of the second LDMOS switch to energize the resistor and causea nozzle chamber to dispense a printing fluid.
 10. The apparatus ofclaim 9, wherein the first LDMOS switch and the second LDMOS switch aren-type devices.
 11. The apparatus of claim 9, wherein the second LDMOSis activated to couple an output of the power supply to the resistor toallow a current to flow through the resistor in response to activationof the HVPMOS switch and deactivation of the first LDMOS switch.
 12. Theapparatus of claim 9, wherein the second LDMOS is deactivated todecouple an output of the power supply to the resistor to prevent acurrent from flowing through the resistor in response to deactivation ofthe HVPMOS switch and activation of the first LDMOS switch.
 13. Theapparatus of claim 9, wherein the power supply coupled to the HVPMOSswitch and the second LDMOS switch are different power supplies.
 14. Amethod comprising: receiving, by a processor, a signal to dispense aprinting fluid from a nozzle chamber; and transmitting, by theprocessor, an enable signal to a first switch and a disable signal to asecond switch coupled to the first switch in a high side switch controlassociated with the nozzle chamber, wherein the enable signal activatesthe first switch and the disable signal deactivates the second switch toallow a voltage to flow through first switch to activate a third switch,wherein the third switch allows a current to flow through to a resistorwhen the third switch is activated, wherein the resistor is to generateheat to dispense the printing fluid from the nozzle chamber.
 15. Themethod of claim 14, further comprising: receiving, by the processor, asignal to stop the printing fluid from dispensing from the nozzlechamber; and transmitting, by the processor, a disable signal to thefirst switch and an enable signal to the second switch, wherein thedisable signal deactivates the first switch and the enable signalactivates the second switch to prevent the voltage from flowing throughthe first switch and to deactivate the third switch to prevent thecurrent from flowing through the resistor.